As is known in the art, the reception and demodulation of desired signals is limited by the presence of high levels of in-band interference. Modern receivers convert analog input waveforms into digital waveforms at some point in order to take advantage of enhanced digital technologies. This conversion process is performed by an analog to digital converter (ADC). As is known in the art, the level of in-band interference that can be tolerated in these digital receivers is often limited by the actual or effective number of bits (ENoB) of this ADC.
Digital post-processing, especially adaptive interference post-processing, can greatly reduce the impact of in-band interference on recovered signal integrity, but only if the ratio of interference to signal levels are within dynamic range limitations imposed by the digitizing ADC's ENoB. When in-band interfering signals are very large, the gain in front of this ADC must be reduced to keep the ADC from saturating. This can reduce the desired signal to the point where ADC ENoB limitations degrade the ability to recover the signal properly. Mono-bit ADC techniques, which utilize a saturating 1-bit “ADC” to generate a 1-bit word sample-stream, avoid these pitfalls, but such techniques reduce the signal-to-noise ratio by approximately 2 dB and break down when one or a few large interferers dominate.
Conventional analog or digital interference cancellation techniques generally rely on frequency, spatial, temporal, or code discrimination to separate interference from desired signals for cancellation purposes. Such techniques generally utilize linear cancellation methods, which reduce signal as well as interference levels when there is near or complete signal-interference coincidence. This is due to lack of orthogonality between the signal and interferer in a linear space as coincidence is approached.
While prior art systems use analog cancellation, this analog cancellation has historically been limited to 20 to 30 dB due to imperfections in and differences between analog components in the analog cancellation path.